#include<iostream>
#include<cstdlib>
#include<ctime>
using namespace std;
int exam4_20()
{
	int x, y, n, num = 0;
	srand(time(NULL));
	x = 100 + rand() % (999 - 100 + 1);
	y = 100 + rand() % (999 - 100 + 1);
	do
	{
		cout << x << "+" << y << "=?\n";
		cin >> n;
		num++;
	} 
	while (n != x + y);
	cout << num << endl;
	return 0;
}